Abstract
The objective of this study is to create modified starch with high RS content (especially heat resistant RS) through the combination of two techniques of restricted hydrolysis and annealing. Native maize starch was partially hydrolyzed in HCl solution at room temperature for 4, 14, 23, and 30h. Then, native starch (NC) and partially hydrolyzed starch (PAH) were annealed (ANN) at 50°C for 24h. The structural, physicochemical, and in vitro digestibility properties were measured. The apparent amylose content (AAC) was slightly increased at low hydrolysis level (HL) whilst decreased sharply at high HL. AAC was almost unchanged after annealing. Intrinsic viscosity, molecular weight and degree of polymerization decreased after PAH treatment whilst increased after ANN. The α-helix/amorphous ratio (AH/AMS) did not change much after PAH although it slightly increased after ANN. Relative crystallinity (DRC) increased slightly at low DH and decreased sharply at too high HL. Furthermore, ANN treatment increased DRC. The crystal pattern (A-type) did not change after PAH and ANN treatment. The gelatinization temperature of starch decreased after double modification. In terms of in vitro digestibility, the content of rapidly digested starch (RDS) increased but resistant starch (RS) significantly decreased after gelatinization pre-treatment. The content of resistant starch (RS) and boiling-stable resistant starch (bRS) increased sharply after PAH and ANN treatment. In particular, the highest bRS reached 24.2% under double treatment. While, the maximum bRS of PAH, ANN, and NC starches were 15.2%, 8.9%, and 4.2%, respectively. Actually, native starch contains poor properties and functions and is not suitable for industrial applications. In fact, the production of chemically modified starch with special technological features or high RS concentration is very interesting. In this study, the combination of the two processing techniques (PAH and ANN) significantly increased RS, especially bRS, which is capable of controlling blood glucose, body weight, and other benefits to human health.
Highlights
apparent amylose content (AAC) decreased at high degree of hydrolysis (DH), especially in samples with hydrolysis time >14 h
The slight increase in AAC of samples with low DH (H4 and H14 samples) compared with native starch (NC) was due to the breakdown of α1,6 glycosidic bonds in the amorphous regions causing the release of linear segments
The color of the starch-iodine complex varies from blueviolet (DP 39-40) to brown (DP 21-24)
Summary
Resistant starch (RS) is not enzymatically digested in the human small intestine (Sajilata et al, 2006). RS has the effect of inhibiting fat accumulation, controls blood cholesterol, and has good effects on diabetes control, obesity reduction, overweight management (Sajilata et al, 2006). According to Mun and Shin (2006), RS increased 1.5 times, compared with native starch, after hydrolysis with 0.1 M HCl for 30 days. Chung et al (2009) showed that the content of RS and boilingstable RS increased significantly under annealing treatment (starch suspension of 30%, w/v; 50oC for 24h). In addition to the formation of RS, some structural and physicochemical properties of modified starch were changed under partial hydrolysis and annealing. Starch had a decrease in average molecular weight.
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